1. Field of the Invention
This invention relates generally to phase shifting, and more particularly to phase array apparatus such as phased array antennas.
2. Description of the Related Art
Phased array apparatus are employed in a variety of applications for transmitting and receiving radar and other types of radio-frequency (RF) signals, and may be implemented in a variety of geometric array configurations. Examples of array configurations include linear arrays, two-dimensional arrays, planar arrays, rectangular arrays and conformal arrays. Phase shifting devices have been employed to alter the phases of signals transmitted or received by individual elements of a phased array apparatus in a binary weighted manner. By altering the phase of signals transmitted or received by individual phased array elements relative to each other the directional orientation of signals transmitted or received by the array may be controlled. Examples of phase shifting devices include digital phase shifting devices (e.g., diode phase shifter using switched-line, hybrid-coupled and loaded-line) and analog phase shifting devices that are digitally controlled (e.g., ferrite phase shifter).
In operation, phased array apparatus may suffer from periodic phase quantization or phase rounding errors which result in phase quantization sidelobes that degrade (raise) the side-lobe levels. Techniques that have been employed in the past to reduce phase quantization errors include the use of random phasing, the introduction of small errors into the feed network of an array, the addition of an extra phase bit, or the incorporation of a parabolic phase taper in the feed. In one particular example, random phasing has been implemented with ferrite or diode phase shifters in narrow band phased array antennas employed for radar applications.